Pwelch and accuracy/number of points

Hello, I have a signal sampled at 200Hz and when I perform the Pwelch method the returning frequency vector is till 100Hz as expected. My interest, though, is only at the frequencies 0-2Hz. Using xlim([0 2]) i can see the frequency content of interest but i want to use more points or maybe downsample my signal in order to get better accuracy at this frequencies. What do you propose?

Answer 1

[Honglei Chen]

If you only need to get more points in pwelch plot, I think increasing the number of FFT points in pwelch should do the trick.

Answer 2

[George Lazaridis]

to be more specific, i have derived the HRV signal (the RR intervals) and i want to see the low and hi frequency content. But when i just plot the PSD returned by the Welch's method, i get a different plot than the one expected.